1. Technical Field of the Invention
This invention is generally related to power conversion and more particularly to regulating a DC to DC converter.
2. Description of Related Art
Power supplies are known to take one voltage level and convert it to one or more different voltage levels and may be designed using a variety of topologies. For example, a power supply may be a switch mode power supply or ferro-resonance power supply. A switch mode power supply may be implemented using one of many switch-mode topologies. For example, a switch-mode power supply may be implemented as a buck converter, a boost converter, a half-bridge converter, or a full bridge converter.
Typically, if a switch-mode power supply is needed to provide a substantially amount of power (e.g. greater than 100 watts), the power supply will include a full bridge or a half-bridge converter. If a switch-mode power supply is needed for lower power applications, it will include a buck or boost converter topology. Generally, a buck converter produces an output voltage that is less than the input voltage while a boost converter produces an output voltage that is greater than the input voltage. Thus, in low power applications such as portable electronic devices, a buck or boost converter is generally utilized depending on the voltage of the power source and the voltage needed to power the circuitry of the portable electronic device.
For example, a portable electronic device may be designed to be powered from a lithium battery that produces a supply between 4.2 volts and 3.0 volts while CMOS integrated circuits in the device requiring a supply of 1.8 volts to 2.5 volts. In this example, a buck converter would be utilized to step down the battery voltage to a controlled 1.8 or 2.5 volts. If, however, the same portable electronic device were designed to be powered from a 1½ volt battery, the device would include a boost converter to step up the 1½ volts to 1.8 or 2.5 volts.
An issue with battery powered portable electronic devices arises when the device transitions from being powered by an external power source (e.g., an AC powered power supply, a battery charger, a USB connection, etc.) to being powered by the battery via a DC to DC converter. In this instance, since the DC to DC converter cannot instantaneously produce the internal supply voltage from the battery voltage, the power supply to the portable electronic devices droops substantially, which would cause noticeable interruption of proper operation of the portable electronic device (e.g., an MP3 player, a PDA, a cell phone, etc.).
Therefore, a need exists for a method and apparatus of regulating a DC to DC converter that powers portable devices to substantially avoid power supply droops during power source transitions.